The background of the invention can be obtained from the Swedish patent SE 521 363 and the corresponding U.S. Pat. No. 6,817,055 showing a method for mounting of a drum and a drum being a part of a shaft as a part of a brush roller. FIG. 5 of these publications shows mounting of two drum segments by a screw running radially through a clearance hole in an external shoulder and into a threaded hole of an internal shoulder. This coupling is a rigid and good coupling for connection of two neighbouring segments but it is hard and time consuming to fit the screw tight against the treaded hole of the internal shoulder during the mounting.